Amphiphilic Conjugates Research Articles

New Amphiphilic Conjugates of Amino–Poly(ethylene glycols) With Lipoamino Acids as Surface Modifiers of Colloidal Drug Carriers

AbstractPoly(ethylene glycol) (PEG2000) polymers containing one or two amine residues are linked to α‐lipoamino acids (LAA) to produce mono‐ and homo‐disubstituted PEG–LAA conjugates as new materials for the surface coating of colloidal drug carriers. Conjugates are characterized by FT‐IR, 1H‐NMR, and MALDI–TOF mass spectrometry. Differential scanning calorimetry studies are performed to assess the interaction of PEG2000–LAAs with a biomembrane model (dipalmitoylphosphatidylcholine multilamellar liposomes). Whereas the parent PEGs affect only the superficial structure of the bilayers, the amphiphilic PEG–LAA conjugates exert a modulated perturbing effect on the thermotropic profile of liposomes. A molar concentration between 5% and 10% is individuated as the more suitable to produce stable vesicles.

Synthesis and Antibacterial Activities of Amphiphilic Neomycin B-based Bilipid Conjugates and Fluorinated Neomycin B-based Lipids

Investigating the effect of lipid hydrophobicity on the activity of amphiphilic neomycin B conjugates, six polycationic amphiphiles (PAs) were created. Four of the new compounds incorporated either palmitic or arachidic di-lipid lysine tails, while two had single fluorinated undecanoic acid tails. The basicity of half of the compounds was increased through the incorporation of six guanidine moieties, in order to assess the effect of base strength on antimicrobial activity. A panel of ten bacteria was used for the testing, with seven strains obtained from the American Type Culture Collection series and three clinical isolates from Canadian Intensive Care Units. When compared to previous results with hydrocarbon monolipids the PAs all compounds were found to have reduced activity, though the hemolytic activity of the compounds with fluorinated tails was sharply reduced, with only a moderate reduction in antimicrobial activity.

3-Helix micelles stabilized by polymer springs.

Despite increasing demands to employ amphiphilic micelles as nanocarriers and nanoreactors, it remains a significant challenge to simultaneously reduce the particle size and enhance the particle stability. Complementary to covalent chemical bonding and attractive intermolecular interactions, entropic repulsion can be incorporated by rational design in the headgroup of an amphiphile to generate small micelles with enhanced stability. A new family of amphiphilic peptide-polymer conjugates is presented where the hydrophilic headgroup is composed of a 3-helix coiled coil with poly(ethylene glycol) attached to the exterior of the helix bundle. When micelles form, the PEG chains are confined in close proximity and are compressed to act as a spring to generate lateral pressure. The formation of 3-helix bundles determines the location and the directionalities of the force vector of each PEG elastic spring so as to slow down amphiphile desorption. Since each component of the amphiphile can be readily tailored, these micelles provide numerous opportunities to meet current demands for organic nanocarriers with tunable stability in life science and energy science. Furthermore, present studies open new avenues to use energy arising from entropic polymer chain deformation to self-assemble energetically stable, single nanoscopic objects, much like repulsion that stabilizes bulk assemblies of colloidal particles.

Controllable self-assemblies of β-cyclodextrin-calix[4]arene couples

Amphiphilic cyclodextrin-calixarene conjugates 1 and 2 were synthesized from “click chemistry”, and their self-assembly behaviors were investigated by transmission electron microscopy, and atomic force microscopy. The results obtained show that 1 and 2 can self-assemble to form distinctly different aggregations, and the morphology of aggregations critically relies on the polarity and hydrophilicity of the solvent.

Synthesis and cellular studies of PPIX-homing peptide conjugates

Five amphiphilic protoporphyrin IX-peptide conjugates bearing the sequences ATWLPPR, AAhexPQRRSARLSA and cERGDPhe conjugated via the propionic side chains, were synthesized and evaluated in vitro using two cell lines: human carcinoma HEp2 and human leukemia HL-60. All conjugates were found to have low dark- and photo-toxicities in both cell lines, and 3 to 10-fold higher accumulation was observed within HL-60 vs. HEp2 cells, depending on the nature of the peptide sequence. The preferential subcellular sites of localization for all conjugates were found to be the lysosomes in HEp2 cells, and the mitochondria in HL-60 cells, suggesting different mechanisms of cellular internalization.

The movement of self-assembled amphiphilic polymeric nanoparticles in the vitreous and retina after intravitreal injection

The purpose of this study is to determine the correlation between the distribution of nanoparticles in the vitreous and retina and their surface properties after intravitreal injection. For this purpose, we synthesized seven kinds of nanoparticles through self-assembly of amphiphilic polymer conjugates in aqueous condition. They showed similar size but different surface properties. They were labeled with fluorescent dyes for efficient tracking. After intravitreal injection of these nanoparticles into a rodent eye, their time-dependent distribution in the vitreous and retina was determined in stacking tissue images by confocal microscopy. The results demonstrated that the surface property of nanoparticles is a key factor in determining their distribution in the vitreous and retina after intravitreal injection. In addition, immunohistochemistry and TEM images of retina tissues suggested the important mechanism related with Mülller cells for intravitreally administered nanoparticles to overcome the physical barrier of inner limiting membrane and to penetrate into the deeper retinal structures. Therefore, we expect that this study can provide valuable information for biomedical researchers to develop optimized nanoparticles as drug or gene carriers for retinal and optic nerve disorders such as glaucoma, age-related macular degeneration, and diabetic retinopathy.

Serum-stable, long-circulating paclitaxel-loaded colloidal carriers decorated with a new amphiphilic PEG derivative

The paper describes sterically stabilized lipid nanocapsules (LNC) and multilamellar liposomes (MLV) coated using a new amphiphilic conjugate of PEG2000 with a 2-alkyl-lipoamino acid (LAA). A complement activation assay (CH50) and uptake experiments by THP-1 macrophage cells were used to assess in vitro the effectiveness of the PEG-LAA derivative of modifying the surface behavior of nanocarriers. Administered to rats or Swiss mice, respectively, the PEG2000-LAA—modified LNC and MLV showed plasma half-lives longer than the corresponding naked carriers.To assess the ability of nanocarriers to specifically reach tumor sites, paclitaxel (PTX)—loaded LNC and MLV were administered subcutaneously to rats implanted with a 9L glioma. Animals treated with saline or naked LNC and MLV underwent a quick expansion of tumor mass, up to a volume of 2000mm3 25 days after the injection of tumor cells. On the contrary, treatment with a PEG-LAA modified LNC carrier reduced the growth of the tumor volume, which did not exceed 1000mm3 by day 25. Analogous positive results were obtained with the liposomal systems. The experimental findings confirmed that these new PEG-LAA conjugates allow to obtain sterically stable nanocarriers that behave effectively and in a comparable or even better way than the (phospho)lipid PEG derivatives commercially available.

Neomycin–phenolic conjugates: Polycationic amphiphiles with broad-spectrum antibacterial activity, low hemolytic activity and weak serum protein binding

Here we present a proof-of-concept study, combining two known antimicrobial agents into a hybrid structure in order to develop an emergent cationic detergent-like interaction with the bacterial membrane. Six amphiphilic conjugates were prepared by copper (I)-catalyzed 1,3-dipolar cycloaddition between a neomycin B-derived azide and three alkyne-modified phenolic disinfectants. Three conjugates displayed good activity against a variety of clinically relevant Gram positive and Gram negative bacteria, including MRSA, without the high level of hemolysis or strong binding to serum proteins commonly observed with other cationic antimicrobial peptides and detergents.

Nanoparticledrug delivery enhances the cytotoxicity of hydrophobic–hydrophilic drug conjugates

We report a drug conjugation approach to concurrently load both hydrophobic and hydrophilic drugs into the same drug delivery nanocarrier in a precisely controllable manner. Using paclitaxel as a model hydrophobic drug and cisplatin as a model hydrophilic drug, we demonstrate the synthesis and characterization of a paclitaxel–cisplatin conjugate via a hydrolysable linker and its easy encapsulation by a lipid–polymer hybrid nanoparticle with controllable drug loading yield and drug release profile. The cytotoxicity of the resulting drug conjugate loaded nanoparticles against human ovarian cancer cells is investigated and compared to that of unencapsulated free drug conjugates. It is found that the cellular cytotoxicity of the hydrophobic–hydrophilic drug conjugates is significantly improved after being encapsulated into the nanoparticles. This is likely because the nanoparticles facilitate the intracellular entry of the amphiphilic drug conjugates and thus overcome their poor transport ability across the lipid bilayer structured cellular membranes.

Edible supramolecular chiral nanostructures by self-assembly of an amphiphilic phytosterol conjugate

We study the self-assembly of a food-grade glucose-β-sitosterol conjugate in bulk and in solution by small angle X-ray scattering (SAXS) and atomic force microscopy (AFM). The amphiphilic behavior of the glucose-β-sitosterol conjugate, combined with the chirality of both its moieties, leads in solutions to the aggregation into supramolecular chiral aggregates with plate-like, spherical and helical ribbon configurations, depending on concentration and solvent quality. Owing to the crucial role of phytosterols in replacing cholesterol content and the need for functional edible fibrils with enhanced nutritional value, this system shows great promise in the struggle for the design of new functional food building blocks with targeted properties.

Engineering of peglayted camptothecin into core–shell nanomicelles for improving solubility, stability and combination delivery

Camptothecin (CPT), a broad-spectrum anticancer drug, is limited in the extensive applications for its extremely hydrophobic property and low physiological stability in clinical use. In this study, prodrug of PEGylated CPT bioconjugate was synthesized to address the above critical issues. The as-designed amphiphilic conjugate could self-assemble into core–shell nanomicelles to enhance the solubility of the CPT and simultaneously improve the stability by encapsulating CPT in the micellar core. Furthermore, the core–shell structure of nanomicelles affords the capability of combination drug delivery by loading other hydrophobic drugs in the core. Doxorubicin (DOX) was chosen as model for combination delivery by physical encapsulation method. It is demonstrated that DOX could be efficiently loaded with controlled release kinetics. Cellular uptake experiments show that this micelle based drug delivery system is able to be efficiently uptaken by cells to achieve combination delivery. In vitro cytotoxicity of the CPT micelles and the DOX-loaded system are evaluated respectively through cell cytotoxicity against Hela cells, the results show an obviously enhanced cytotoxicity over free CPT while the DOX-loaded system exhibit more potent inhibition on cell proliferation ascribed to the combined effect of physically entrapped DOX and chemical conjugated CPT.

Enzymatically triggered multifunctional delivery system based on hyaluronic acid micelles

Tumor targetability and stimuli responsivity of drug delivery systems (DDS) are key factors in cancer therapy. Implementation of multifunctional DDS can afford targetability and responsivity at the same time. Herein, cholesterol molecules (Ch) were coupled to hyaluronic acid (HA) backbones to afford amphiphilic conjugates that can self-assemble into stable micelles. Doxorubicin (DOX), an anticancer drug, and superparamagnetic iron oxide (SPIO) nanoparticles (NPs), magnetic resonance imaging (MRI) contrast agents, were encapsulated by Ch–HA micelles and were selectively released in the presence of hyaluronidase (Hyals) enzyme. Cytotoxicity and cell uptake studies were done using three cancer cell lines (HeLa, HepG2 and MCF7) and one normal cell line (WI38). Higher Ch–HA micelles uptake was seen in cancer cells versus normal cells. Consequently, DOX release was elevated in cancer cells causing higher cytotoxicity and enhanced cell death.

Redox-sensitive micelles self-assembled from amphiphilic hyaluronic acid-deoxycholic acid conjugates for targeted intracellular delivery of paclitaxel

A targeted intracellular delivery system of paclitaxel (PTX) was successfully developed based on redox-sensitive hyaluronic acid-deoxycholic acid (HA-ss-DOCA) conjugates. The conjugates self-assembled into nano-size micelles in aqueous media and exhibited excellent drug-loading capacities (34.1%) and entrapment efficiency (93.2%) for PTX. HA-ss-DOCA micelles were sufficiently stable at simulated normal physiologic condition but fast disassembled in the presence of 20 m m reducing agent, glutathione. In vitro drug release studies showed that the PTX-loaded HA-ss-DOCA micelles accomplished rapid drug release under reducing condition. Intracellular release of fluorescent probe nile red indicated that HA-ss-DOCA micelles provide an effective approach for rapid transport of cargo into the cytoplasm. Enhanced cytotoxicity of PTX-loaded HA-ss-DOCA micelles further confirmed that the sensitive micelles are more potent for intracellular drug delivery as compared to the insensitive control. Based on flow cytometry and confocal microscopic analyses, observations revealed that HA-ss-DOCA micelles were taken up to human breast adenocarcinoma cells (MDA-MB-231) via HA-receptor mediated endocytosis. In vivo investigation of micelles in tumor-bearing mice confirmed that HA-ss-DOCA micelles possessed much higher tumor targeting capacity than the insensitive control. These results suggest that redox-sensitive HA-ss-DOCA micelles hold great potential as targeted intracellular delivery carriers of lipophilic anticancer drugs.

Synthesis of novel amphiphilic conjugates with a biological recognition function for developing targeted triggered liposomal delivery systems

Several novel amphiphilic lipid derivatives were synthesized consisting of a lipid anchor connected to the hydrophilic moiety via a disulfide or glycoside bond and biotin linked to the hydrophilic part. Disulfide bonds were established by the help of 4-phenyltriazol-3,5-dione. Dansyl or fluorescein was covalently linked as fluorescent marker to some of the conjugates, allowing spectroscopic and microscopic detection. The conjugates represent first amphiphilic lipids carrying all four functions, i.e., lipophilic, hydrophilic, recognition, and disulfide cleavage group in one molecule, which are necessary for targeted, triggered drug delivery from phospholipid liposomes on demand.

Enhancement of surface ligand display on PLGA nanoparticles with amphiphilic ligand conjugates

Biodegradable polymeric nanoparticles are widely recognized as efficacious drug delivery vehicles, yet the rational engineering of nanoparticle surfaces in order to improve biodistribution, reduce clearance, and/or improve targeting remains a significant challenge. We have previously demonstrated that an amphiphilic conjugate of avidin and palmitic acid can be used to modify poly(lactic-co-glycolic acid) (PLGA) particle surfaces to display functional avidin groups, allowing for the facile attachment of biotinylated ligands for targeting or steric stabilization. Here, we hypothesized that the incorporation, density, and stability of surface-presented avidin could be modulated through varying the lipophilicity of its fatty acid conjugate partner. We tested this hypothesis by generating a set of novel conjugates incorporating avidin and common fatty acids. We found that conjugation to linoleic acid resulted in a ~ 60% increase in the incorporation of avidin on the nanoparticle surface compared to avidin–palmitic acid, which exhibited the highest avidin incorporation in previous studies. Further, the linoleic acid–avidin conjugate yielded nanoparticles with enhanced ability to bind biotinylated ligands compared to the previous method; nanoparticles modified with avidin–linoleic acid bound ~ 170% more biotin–HRP than those made with avidin–palmitic acid and ~ 1300% more than particles made without conjugated avidin. Most critically, increased ligand density on anti-CD4-targeted nanoparticles formulated with the linoleic acid–avidin conjugate resulted in a 5% increase in binding of CD4 + T cells. Thus we conclude that the novel avidin–linoleic acid conjugate facilitates enhanced ligand density on PLGA nanoparticles, resulting in functional enhancement of cellular targeting.

An Amphiphilic Conjugate Approach toward the Design and Synthesis of Betulinic Acid–Polyphenol Conjugates as Inhibitors of the HIV‐1 gp41 Fusion Core Formation

Exploration of potent inhibitors of the HIV-1 gp41 fusion core formation is a promising strategy to discover small-molecule HIV-1 entry inhibitors for the treatment of HIV-1 infection. In this paper, a series of novel betulinic acid-polyphenol conjugates was designed, guided by molecular modeling of the binding of betulinic acid (BA) and phenolic galloyl/caffeoyl groups in the groove on the gp41 N-terminal heptad repeat (NHR) trimeric coiled coil. These conjugates were synthesized via conjugation of galloyl and caffeoyl groups with BA at the C-28 position. Their inhibitory activities of HIV gp41 six-helix bundle (6-HB) formation between the NHR peptide N36 and the C-terminal heptad repeat (CHR) peptide C34 were evaluated with size-exclusion HPLC. Conjugates bearing a galloyl group were found to exhibit four to sixfold higher inhibitory activities than that of parent compound BA, suggesting that they may be exploitable as HIV-1 fusion/entry inhibitors targeting gp41. The docking study on BA and its derivatives suggests that hydrophobic and hydrogen-bonding pockets exist in the groove of the gp41 NHR trimeric coiled coil and that a potent inhibitor should have amphiphilic structures to cooperatively interact with both pockets. This possibility was explored by incorporating both lipophilic and hydrophilic groups into the conjugates in a well-defined orientation to bind with both pockets in the gp41 NHR-trimer.

Low molecular weight heparin-all-trans-retinoid acid conjugate as a drug carrier for combination cancer chemotherapy of paclitaxel and all-trans-retinoid acid

As a novel nanocarrier for simultaneous delivery of multiple anticancer drugs, low molecular weight heparin-all-trans-retinoid acid (ATRA) (LHR) conjugate was developed. Amphiphilic LHR conjugate had markedly lower anticoagulant activity, and could self-assemble to form nanoparticles for loading hydrophobic drugs. The critical aggregation concentrations of LHR conjugates were varied from 407 to 40mg/L. Paclitaxel (PTX)-loaded LHR nanoparticles were prepared by the dialysis method, with particle sizes in the range of 228.0–108.9nm. The maximum drug-loading was as much as 33.1% with an entrapment efficiency of 93.1%. They displayed enhanced PTX-induced cytotoxicity to HepG2 cells compared to PTX solution. Hemolysis and cytotoxicity studies showed that LHR conjugate was a safe material for intravenous administration. Moreover, the pharmacokinetic profiles indicated that PTX-loaded LHR nanoparticles contributed to an extended circulation of PTX and ATRA. These results suggest that PTX-loaded LHR nanoparticles can be considered as promising anticancer drug delivery system for combination chemotherapy.

Self-aggregates of cholesterol-modified carboxymethyl konjac glucomannan conjugate: Preparation, characterization, and preliminary assessment as a carrier of etoposide

Various cholesterol (CH) bearing carboxymethyl konjac glucomannan (CKGM) amphiphilic conjugates (denoted CHCKGM) were synthesized using CKGM as hydrophilic segments and CH as hydrophobic parts. Structural characteristics of these CHCKGM conjugates were investigated using FTIR, 1H NMR and thermogravimetric analysis (TGA). The properties of these self-aggregates were analysed by dynamic laser light-scattering (DLS), zeta potential, transmission electron microscopy (TEM) and the fluorescence probe technologies. The critical aggregation concentration (cac) of CHCKGM conjugates (2.59×10−3 to 5.89×10−3mg/mL) was comparatively low, suggesting that the cholesterol fragment was very effective for forming aggregates. Etoposide was physically entrapped into the CHCKGM nanoparticles by sonication method. The in vitro release behavior of etoposide from CHCKGM nanoparticles revealed a sustained release property. Furthermore, these self-aggregated nanoparticles showed pH- and ionic strength-dependent properties which caused a considerable change in their radius.

Comparative study of photosensitizer loaded and conjugated glycol chitosan nanoparticles for cancer therapy

This study reports that tumor-targeting glycol chitosan nanoparticles with physically loaded and chemically conjugated photosensitizers can be used in photodynamic therapy (PDT). First, the hydrophobic photosensitizer, chlorin e6 (Ce6), was physically loaded onto the hydrophobically-modified glycol chitosan nanoparticles (HGC), which were prepared by self-assembling amphiphilic glycol chitosan-5β-cholanic acid conjugates under aqueous conditions. Second, the Ce6s were chemically conjugated to the glycol chitosan polymers, resulting in amphiphilic glycol chitosan-Ce6 conjugates that formed self-assembled nanoparticles in aqueous condition. Both Ce6-loaded glycol chitosan nanoparticles (HGC-Ce6) and Ce6-conjugated chitosan nanoparticles (GC-Ce6) had similar average diameters of 300 to 350 nm, a similar in vitro singlet oxygen generation efficacy under buffer conditions, and a rapid cellular uptake profile in the cell culture system. However, compared to GC-Ce6, HGC-Ce6 showed a burst of drug release in vitro, whereby 65% of physically loaded drugs were rapidly released from the particles within 6.5 h in the buffer condition. When injected through the tail vein into tumor bearing mice, HGC-Ce6 did not accumulate efficiently in tumor tissue, reflecting the burst in the release of the physically loaded drug, while GC-Ce6 showed a prolonged circulation profile and a more efficient tumor accumulation, which resulted in high therapeutic efficacy. These comparative studies with drug-loaded and drug-conjugated nanoparticles showed that the photosensitizer-conjugated glycol chitosan nanoparticles with excellent tumor targeting properties have potential for PDT in cancer treatment.

Highly Enantioselective α-aminoxylation Reactions Catalyzed by Isosteviol-proline Conjugates in Buffered Aqueous Media

Chiral amphiphilic conjugate catalysts were designed and synthesized by covalently connecting l-proline with an inexpensive natural product, isosteviol. These catalysts demonstrated remarkable efficiency in the asymmetric α-aminoxylation of aldehydes and ketones using nitrosobenzene in phosphate buffer solution, resulting in good to high yields and excellent enantioselectivities without using any additives. At pH 9.1, the amphiphilic catalysts showed a pH responsive ability in phosphate buffer solution, which facilitated the excellent O-selectivity reactions, illustrating a viable approach for the development of asymmetric supra-molecular catalysts.